1. Field of the Invention
The present invention relates to wellbore fluids having improved lubricating properties for use as drilling fluids.
2. Related Art
The most common method of drilling oil wells is one known as the hydraulic rotary drilling method. This method consists of rotating a cutting bit, comprising individual cone bits, which is attached at the bottom of a hollow drill string of the pipe and drill collars to progressively chip away the layers of earth. It has long been the practice to circulate a drilling fluid down through the hollow drill pipe, across the face of the drill bit and upward through the drill hole, to clear the teeth of accumulated dirt, and thence out into the annulus formed between the wall of the well which is being drilled and the exterior of the drill string. The principal functions of this process are to wet and lubricate the bit and drill pipe and to clean the hole bottom by carrying away the cuttings. In certain instances the drilling fluid may also serve to deposit an impermeable wall cake, to prevent caving of the formation from hydration of water-soluble shales and to overcome formation pressures.
There are several types of wellbore fluids used in drilling workover, completion, etc. Briefly, these are oil, oil-in-water emulsions, water-in-oil emulsions, predominantly aqueous fluids, which include clear water, brines (from about 1 weight % soluble salts through saturated solutions) aqueous clay based (called muds), and air (sometimes called foams). Because of the multiplicity of functions which drilling fluids must serve, they are usually comprised of a basic heat transfer and lubricating fluid in which is dispersed one or more additives to modify the properties of the formation being drilled through and therefore the secondary functions which the drilling fluid must also serve. It may contain materials to increase density, to change viscosity, seal the formation, reduce fluid loss, scavenge contaminates, stabilize formation shale and clays, emulsify, inhibit corrosion, inhibit bacteria, lubricate and flocculate.
The environment of the wellbore is, to say the least, hostile, in that extremes of heat and pressure are often encountered, with the multitude and complexity of the problems to be encountered and handled (primarily by the drilling fluid) as diverse as the formations drilled.
The problem to which the present invention is directed is as serious and costly as any other, however, not so dramatic as a blowout or as common as fluid loss (to the drilled formation). The problem here addressed is the seizing of the pipe string in the wellbore. When this occurs, the well may be lost since it is not possible to drill further. When this happens, it may be possible to use some of the available "fishing tools" to free the pipe, however, most likely the pipe and bit are lost and a new bore is drilled.
The seizing of the string can readily occur because the string is not straight in the bore but makes constant contact with the sides of the bore as the string is rotated. There may be several points of contact and any one or more of these may bind with the wall of the bore or increase the torque on the string.
It is an advantage of the present invention, that the seizing or binding of the drill string in the wellbore is reduced or eliminated and torque and drag are reduced. It is a further advantage of the present invention that the drill string is lubricated in the wellbore to facilitate rotation. It is a feature of the present wellbore fluids that they have improved lubrication to other similar fluid. It is a further advantage of the present wellbore fluids that improved lubrication is not obtained at the loss of other desired characteristics of the fluids. A further advantage of the present invention is that oil wetting (foaming) is relatively low.